Re: So You Think You Can Const?

Julio Di Egidio <julio@diegidio.name> writes:

On 11/01/2025 12:14, David Brown wrote:
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On 10/01/2025 19:56, Keith Thompson wrote:

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<snip>
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The idea was to place the emphasis on "free" changing the pointer,
rather than the data pointed to.

>
I feel I am still altogether missing the point.
>
Is my understanding correct that when freeing a pointer: 1) the
pointer value, i.e. the address it holds, does not change;  OTOH, 2)
the pointed-to object does change, in the sense that it is marked
unusable (and, supposedly, made available to re-allocation)?

Not exactly.  The bits in the pointer don't change.  The _meaning_
of those bits, which is to say what address the bits correspond to,
or even if there is a corresponding address, _does_ change, in the
sense that any attempt (in a C program) to look at the bits as an
address is -- as far as the C standard is concerned -- completely
unpredictable.

Moreover, while the pointer value has not changed, it is in fact
changed in the sense that it has become invalid, namely the pointer
cannot be used (validly dereferenced) anymore.  Not just that, but
*every* pointer to the same object, i.e. holding the same address, has
become invalid.

It isn't just that those pointers cannot be dereferenced.  Even
trying to load their values might blow up the program, or even do
anything else one might imagine.